One known type of electronic control module is a high cost module providing a large range of facilities and uses a sophisticated microprocessor for carrying out all the control tasks of the module.
Another known type of electronic control module is a low cost module, for use in cheaper vehicles, which only provides some of the features of the more expensive version. This electronic control module uses a less sophisticated, and thus less expensive, microprocessor.
Recently, attempts have been made to provide a low cost, high function control module. GB-A-2,173,611 discloses an electronic control module in which two microprocessors share the various tasks of the control module and can also provide a back-up facility when one of the processors fails. The tasks have generally been divided so that one of the processors deals with fuel injection and the other with spark ignition.
A problem with such a division of the tasks is that the processors need to communicate between one another a substantial amount and some of the data communicated is time critical, which requires a high-speed communications line.
Furthermore, both processors must carry out both time critical and non-time critical operations which makes their programming more complex and requires both of the processors to be of a greater capacity than is otherwise necessary.
Another problem, as a result of both processors being connected to a plurality of auxiliary components, is that both processors are equally as likely to fail, which requires a complex back-up system to detect failure of one of the processors and effectively to replace it.
The present invention seeks to provide an improved electronic control module.
According to an aspect of the present invention, there is provided an electronic control module for a vehicle comprising a first processor adapted to calculate fuelling requirements of the engine and spark advance on the basis of engine operating conditions, and a second processor adapted to initiate fuel injection and ignition on the basis of engine position.
By dividing the tasks so that one processor carries out the required calculations and the other the triggering of fuel injection and start of combustion, it is possible to reduce significantly the amount of processing that is required. It is therefore possible to use significantly simpler processors.
Another advantage of this arrangement is that, in appropriate embodiments, it will not be necessary to access the second processor. Thus, an engine or powertrain calibration engineer, for example, would only have to access the first processor, making his task considerably simpler. Furthermore, this can also reduce the cost of the module significantly since an on-board ROM can be used for the second processor rather than an expensive EPROM or other such memory.
Furthermore, it is possible to ensure that the tasks and auxiliary components which are most likely to fail are only associated with the first processor, so if a back-up facility is to be provided, this can be done in connection with the second processor only, making the facility relatively simple to implement.
Preferably, there are only two processors.
The first processor may also be adapted to control the idle speed of the engine.
Preferably, the second processor is adapted to determine spark dwell timing on the basis of engine position and engine operating conditions. Thus, the second processor can be thought of as providing timing triggers, while the first processor carries out the required calculations, together with the functions requested and calibrated by the customer, or service engineer.
The electronic control module may also include a back-up mode to enable it to continue operating even on failure of the first processor or of any of the components associated with the first processor. Thus, in an embodiment, the electronic control module comprises means to generate a check signal representative of the state of operation of the first processor and/or of any components associated with the first processor, the second processor being adapted to control the operation of the engine when the check signal indicates failure of the first processor and/or of any components associated with the first processor.
In a practical embodiment, there may be provided a first memory containing data representative of fuelling requirements at a plurality of engine speeds, the second processor being adapted to access the first memory on failure of the first processor and/or of any components associated therewith. There is preferably also a second memory containing data representative of spark advance at a plurality of engine speeds, the second processor being adapted to access the second memory on failure of the first processor and/or of any components associated therewith
In a preferred embodiment, the data representative of fuelling requirements and spark advance is based on engine speed and also on engine load, represented for example by throttle position
The first and second memories may be incorporated in the same physical memory, and are preferably incorporated in the second processor.
Failure of the first processor is generally more likely due to the variety of functions it has to perform and due to the components to which it is connected.